Steel



Patented May 19, 1925.

UNITED STATES PATENT orsics,

PROCESS OF TREATING STEEL.

No Drawing.

To all whom it may concern:

Be it known that I, Hmosrrr SHIOKAWA, a subject of the Emperor of Japan, and resident of 18 Nichom-e, Dainichidori, in the city of Kobe, in the Prefecture of Hyogo and Empire of Japan, have invented a new and useful Process of Treating Steel, of which the following is a specification.

lhis invention relates to a process of treating steel, more particularly to the treating of shaped steel bodies formed by rolling, forging" or in any other manner, and the invention has for its object to provide, in a manner as hereinafter set forth, a process of treating steel bodies to improve the quality and mechanical properties thereof.-

hat is meant by quality and mechanical properties is that the body of steel treated by the present process has its quality im proved by making it of a uniform structure throughout, and by imparting to it proper degrees. of elongation and toughness with a very small loss of tensile strength, and further by driving off the occluded gases therefrom with consequent elimination of undue brittleness, whereby the elongation and toughness are considerably increased While preserving the desirable degree or amount of tensile strength attributable to the elimination of the internal stresses and stra ns and absorbed gases from the steel body.

The process comprises the conveying the body of steel to a suitable enclosure While the same still retains excess of heat ranging from 500 to 700 degrees centigrade, disposing'the same under conditions calculated to prevent said excess of heat from radiating and being lost to no purpose and to produce uniform temperature throughout its entire ass, causing it to cool very slowly after maintaining said uniform temperature for a certain length of time, and taking it out on its being completely cooled. The primary object of this invention is to save the cost and time required in the usual reheating system of annealing and to provide an excellent steel body With perfectly uniform structure economically and easily without any lossof qualities of steel incident to said reheating system of annealin Other objects and advantages to be derived from the use of this invention will be Application filed August 26, 1922. Serial No; 584,550.

point (usual annealing temperature) of steel by utilizing the excess of heat retained by it and then causing it to cool slowly,

without any resort to the reheating system or annealing hitherto 111 practice in various countries, and so the process has a very Wide range of application with consequent modifications in details of design and practice according to ingredients, sizes, etc., of the body of steel to be treated, and it may be quite clear that those modifications that come Within the sphere of the append-ed claims all fall under the spirit of my invention; but to avoid unnecessary confusion and make the invention easy to understand for one skilled in the art to which it appertains, I will specifically describe the method of applying it to the final or qualipy treatment of steel plates as an example, tins:

As the first step, a slow-cooling pit is from 500 to 700 degrees centigrade, and just at this moment the plate is conveyed into the slow-cooling pit prepared in the manner referred to hcreinbefore to prevent lowering of its ten'iperature, and another plate is put into and laid on the first one, and so on, until a suitable number of plates are superposed, and finally some lime is spread over the pile; and then a cover or door is placed on the top of the pit and hermetically sealed so as to thoroughly insulate the interior from the atmosphere; and, if said plates are left in this state'for 20 to 48 hours or more (length of time being determined by the size and thickne of the steel plate), each plate becomes perfectly uniform in temperature throughout its entire length and sectional area, that is, the entire mass, owing to the fact that the excess of heat of the plate is retained in the interior of the pit, and, since suitable amount of energy is imparted to the steel plate, its internal stresses are thoroughly removed, gas or gases previously ah sorbed in the steel mass are completely driven off, and the entire structure made uniform throughout, and then the plate is slowly cooled, so that there is no possibility for such gas or gases to be re-absorbed or mechanical'stresses to reappear, with the rcsult that the qualities and mechanical properties of the finished plate are perfectly nor malized and improved. By my improved process, loss of qualities of steel attributable to direct heating at high temperatures as in the case ofthe usual'reheating system of annealing is perfectly eliminated, and, since it does not require any reheating, cost and labor attending to such reheating can be dis-- pensed with, which means a decided advantage over the usual system of annealing. Experiments conducted by me show that a steel plate treated by my improved process possesses an elongation coellicient higher than a similar plate freely cooled in the air by. 3 to 8 per cent, and has, in addition, an important feature of being free from breakage or rupture.

As. it is necessary to prolong or shorten length; of time for maintaining the required uniform temperature and for slow-cooling, so is it needed to adjust time of treatment to meet various requirements, when applying my present invention to bodies of steel other thanplates, according as such body is greater or smaller than the plate, which fact may be readily understood. When the artie es to be treated are of great bulk, it is often advisable to treat oneor a few at a time. In, short, it is necessary to modify modes of ap plication, though strictly on the same principle, more or less to adapt the invention to particular needs, which modifications may be done with ease, provided that full understanding of the principle underlying my invention is once obtained.

I am aware that there is a. kind of. furnace for equalizing the temperature of a steel ingot'throughout its entire mass to prepare it for rolling and other operations when its interior is too hot, and another furnace for preparing a cold body of steel or asteel ingot too cold to be rolled at once for such operations by heating it uniformly throughout its entire mass, strictly on the principle of the first-mentioned furnace, as may be inferred from the following quotation from Iron and Steel by Erik Oberg and Franklin D. Jones, First Edition, pp. 1% to 147, pub-- lshed by the Industrial Press, New York I viitvz Soaking Pits :As the outside of the ingot cools more rapidly than theinside, the inside may be too hot to be rolled or hammered when the outside is hard. The ingot must, therefore, be brought to a uniform heat, which is done by placing it in the soaking pit. This is a covered brick-lined well in which the ingot is stood on end. It retains the heat of previous ingots, so that the excess of heat in the interior of the ingot placed in it soaks through the mass but is not lost. for the mill without the consumption of any fuel. In addition, the waste of iron due to oxidation of the outer crust of ingot is very slight, because the little atmospheric oxygen in the pit at the beginning is not renewed as it is in a furnace. Later forms of soaking pits, however, are heated by regenerative furnaces, so as to give greater flexibility to the system. In one plant the soakingpit consists of four holes, in each of which six ingots may be placed at one time.

lilither of the two heat-equalizing furnaces referred to hereinbefore has the sole As a result, the steel is prepared object of making the steel material fit for rolling and some other operations by treatlng 1t at temperatures ranging from 1100 to 1 00 degr es centigrade. ln other words,

either of the two types aims at equalizing the ten'iperature of the steel material under treatment throughout its entire mass, this temperature being much higher than the A transforinalion point of-steel, and it is quite obvious that neither has the least consideration for preventing these strains and internal stresses which may be produced in the steel during the rolling or similar operation or while cooling. And, since it is usual for the steel ingot treated in either type of furnace to arrive at a condition suitable for the intended operation in 20 to 60 minutes, it is also very clear that the furnace is under 'no condition to cool slowly; on the contrary,

its sole purpose is to cool the steel as quickly as possible to render it suitable or to heat it as rapidly as possible to make it suited to said operation. quite different from my present invention, in fundamental principles, which treats steel after it is formed into proper shape to eliminate its defects and impart desirable qualities and mechanical properties thereto.

My present invention diifers from either of said two heat-equalizing furnaces or soaking pits in the following essentials:

(1) My present invention has for its object to equalize or normalize qualities and mechanical properties of steel after it is formed, while the furnaces above mentioned treat the steel material itself previous to the forming or shaping operation so as to render such material workable.

My present invention has as one essential condition to equalize the temperature in short, such a furnace is of a steel, semi-manufacture both inside and outside, at a temperature lower thanthe A transformation point of steel, while the furnaces above mentioned are conditioned to equalize temperature of steel material at a temperature higher than said A transformation point. l

(8) My present invention aims at mparting effects similar to or even superior to those obtained by the usual system of annealing, by causing temperature of the steel body throughout its entire mass to equalize at about 400 to 500 degrees centigrade and then maintaining this uniform temperature for a certainlength of time, while the furnace has the sole purpose of rendering steel material itself suitable for working orshaping operation in as short a time as possible.

From the said three items, it is as clear as day that my present invention is quite different from the furnace both in principle and objects, and there may be no room for the least doubt. Though the slow-cooling pit referred to hereinbefore as an example of practice of my present invention is somewhat similar to the soaking pit in form, yet with my invention the slow-cooling pit is nothingbut a means of practising the principle underlying the same, and utilization of the excess of heat and improvement of the qualities and .mechanical properties at temperatures lower than the A transformation.

point of steel are quite different from the object of the heatequalizing furnace, and it will be readily seen that my' invention is utterly independent of said furnace.

The novelty and utilityof my present in-' vention will be understood more definitely and clearly, by comparing the same with various kinds of heat-treatments of steel hitherto in use. To be precise in this connection, I shall quote the following definitions from Engineering Steels by Leslie Aitchison, pp. 39, published by Macdonald & Evans, London, thus:

(1) Normalizing.--Normalizing means heating a steel (however previously treated) to a temperature exceeding its upper critical range, and allowing it to cool freely in the air. p

(2) Annealing.-Annealing means re heating, followed by slow cooling. Its purposes may be:

(a) To remove internal stress, or to produce softness, in which cases the maximum temperature may be arbitrarilychosen.

(7)) To refine the crystallized grains n addition to the above'(a), in which case the temperature used must exceed the upper critical range as in normalizing.

(3) "Hardcning.Hardening means heating a steel to its normalizing temperature, and cooling more or less rapidly in a suitable medium, e. g., water, oil, or air.

(5) Softening.Softening is to facilitate the machining of a steel, and is carried out by annealing or tempering. or both.

(A) Difference between my invention and normalizing: The object of normalizing is to remove stresses, strains or similar abnormal state produced within the steel while the same is undergoing rolling, hammering, drop-forging, casting and other operations. Though it may be considered that this heat-- treatment resembles my present invention in some respects,'yet the former has for its condition to reheat steel, previously treated, to a temperature exceeding the upper critical range and then to cool it freely in the air, while the latter is conditioned to treat a steel body at a ten'iperature lower than the lower critical range and then to cause it to cool slowly in the slow-cooling pit insulated from the outer air, and so it is quite obvious that the two processes differ fundamentally from each other from the viewpoint of metallurgy, to say nothing of the fact that the latter has a special feature of attaining the object economically by utilizing excess of heat of the article under treatment.

(B) Difference between my invention and annealing: Annealing aims at removing internal stresses or refining the crystalline structure in addition to said removal of internal stresses. (Vhen removal of internal stresses alone is the object aimed at, the maximum temperature may be arbitrarily decided, but, when removal of internal stresses and the improving of the structure of the crystallized grains'are to be accom plished at once, treating the steel at a tem perature exceeding the upper-critical range is an essential condition. In either case, reheating of the steel manufacture or product to a certain ten'iperature is absolutely necessary. My present invention may seem to resemble somewhat annealing in the results obtained, but in the fundamental principles and modes of operations both ditler much, as may be seen from the following statement (1) Difference between my invention and annealing having its sole object to remove internal stresses :(a) My invention has a special feature of improving qualities and mechanical properties of the steel manufac 'ture or semi-manufacture treated economically by utilizing the excess of heat of the article itself, while the latter process has the defect of requiring reheating with consequent loss of time and labor as well as fuel. (6) Y'Vith my invention, the temperature at (4) "Tempering.Temperingmeansheatwhich to treat the steel body is limited to.

ion

a range of lOO to 500 degrees centigrade for uniformity and said temperature is obtained; auton iatically, so that any person can practise it with ease and. security of results, while in the latter process the maximum temperature is not certain with. consequent difficulty of dete mining the suitable temperature for a particular article. to be treat.-

ed, in addition to the fact that good: results can be obtained by skillful persons alone. My invention can accomplishthe double object of removing internal stresses and improving the structure of the crystallized: grains by one operation, but the latter can only remove internal stresses or to soften the steel. I

(2) Difference between my invention and annealing aiming." at removal of internal stresses and refining of crystalline structure at once :-(=a.) My invention. has the advantage of being able to improve qualities and 1116Ch21111021l properties of steel producteconomically by utilizing the excess of heat a special feature oibcing able to eliminate detects alone and to retain usefulqualities-at the same time owing to the fact that no reheating is necdedto nnpair qualities of steel,

but in the latter process it is essential to reheat the steel to a temperature exceeding the; upper critical range with consequent resuit that the steel is transformed more than is really required, producing loss of some of the desirableproperties and impairment otthesteel dueto direct. heating.

- In a word, thet'undamental diilierenceloo-- tween my invention and annealing hes 1n.

the. fact that in'my. invention the excess of heat is utilized to accomplish the objects in-.

view, and that treatment oi the steel. body is carried out with better results than those of the reheating system. of annealing, at a temperature lower than: A transformation.

point of steel; in other words, ny inventioni combines novelty and utility which cannot. be found in the annealing process (G) Dilii'erence between my invention and tempering; The object: of tempering-3 is to heat the steel to a temperature lower than the carbon-changepoint (A? transformation point), when the steel, previously. hardened.

has been. completely changed to solid solution, which is especially the case withspecial steels, and become too. hard and brittle, to render it softer or a little tougher, and the treatment may. seem to have some points in common withmy invention at first thought, but on. closer observation it will be readily J foundthatthey dilieu remarkably in the following respects:

(a) My invention has asv one of itsconditions to utilize excess of heat of the steel.

under treatment, while the latter requires. reheating.

(1)) My invention has as its object to remove internal stresses and improve qualities and mechanical. properties of the steeltreated, while the latter. aims at changing the steel from solid solution to mixture of fer.- rite and pearlite to reduce its hardness, a very remarkable diliferenee.

, My invention. has an advantage of treating steel at a suitable temperature and then slowly cooling it so as to enable the treated article to retain its desirable qualir ties impartedv thereto by the low-temperaturetreatinent, while in tempering no slowcooling is employed, and: it is clear that they differ in this point, too. r

(d).- Since the temperature for treatment is limited; toirom 400 to 5G0 degrees centigrade in the case of my invention, there is no need of special-care and trouble in this respect, while in. tempering the treating temperature occupies a very wide range from roomtemperature to that slightly. lower than the'A transformation point with consequent trouble and drawbacks "for practical purposes.

In short, my invention combines the three conditions of (1) accomplishing the desired results economically by utilizing the excess of heat, of renderingdetermination of the suitable temperature for treatment ex tremely simple, and of enabling the-article treated to retain desirable qualities and characteristics, while tempering possesses none of said three features, and it will' be readily seenthat there is a fundamental ditlerencebetween these two: processes, and that my invention has perfect novelty and utility quite independent of the tempering;

(D) Difference between my invention and 7' sottening: Softening is a kind. of heattreatment aiming at rendering steel easy to machine, and is carried. out by either an nealing or tempering, or by. both. The ditiierence between my invention and annealing and that between my invention andtempering. have been treated in detail hereinbetore, and so the ditlerence between my invent-ion andsofteningmay be quite clear without any further explanation.

The above-mentioned specific description is enough, I believe, to give one skilled in the art to which it appcrtains a full understanding of my present invention, and to prove the fact that my invention has novelty and utility quite independent ot" any of the said kinds of heat-treatments.

Having thus tullv describedmv invention. what I claim asnew and. desire tosecure by luctter-s Patent" lS-Z.

i no

1. A process oftreating steel comprising the placing of a body'of rolled or forged steel While it still retains-an excess of heat remaining after the working operation, at a temperature below the transformation point in a hermetically sealed enclosure free of direct heating for said body, then allow- 111g said body to remain 1n sa1d enclosure for the placing of a body of rolled'or forged steel while it retains an excess of heat remaining after the working operation ranging from 500 to 700 degrees centigrade in a hermetically sea-led enclosure for a predetermined period to equalize such excess of heat at a uniform temperature to remove internal stresses and gases from said body to provide a uniform structure throughout, and then slowly cooling said body in said enclosure.

3. The process'of improving qualities and mechanical properties of a rolled or forged steel body consisting in conveying the same, while it still retains an excess of heat remaining after the working operation ranging from 500 to 700 degress centigrade, into a slow-cooling pit previously kept at a temperature higher than 400 degrees centigrade but lower than 700 degrees centigrade until suitable quantities ofsuch bodies are reached, spreading lime over the upper layer or portion at the end of said conveying operation, then insulating the interior of said pit from the outside air so as to equalize the temperature of said bodies at about 400 degrees centigrade throughout the entire mass, and finally causing the same to cool slowly, substantially as and for the purposes set forth.

4- A process of treating steel comprising the conveying of a body of rolled or forged steel, while it retains an excess of heat remaining after the working operation ranging from 500 to 700 degrees centigrade, into a cooling pit at a temperature lower than 700 degrees centigrade, then spreading a covering of lime over said body, then providing for the equalizing of the temperature throughout said body to about 400 degrees centigrade, and then slowing cooling the body within the pit.

In testimony whereof'I affix my signature hereunto.

HIROSHI SHIOKAWA. 

